In the prior art, overload protectors have been used with compressor motors in air conditioners or the like for the protection of the motor by sensing any abnormal heat generation or high electrical current situation. Such a situation arises often when the motor is over worked or the rotor is in a locked position.
FIG. 6 shows such a prior art motor protector 101 which has an adjusting screw 103 in the shape of a column at the center of casing 102 made from an electrically insulating material such as a plastic resin. A cylindrical bimetal disk 104 is attached at the top of adjusting screw 103 with movable contacts 105 and 106 provided at both edges of bimetal disk 104.
Mounted in the bottom of casing 102 are two fixed contacts 107 and 108 positioned to be contacted by movable contacts 105 and 106. Additionally, fixed contact 107 is connected to a heating element 109. Motor protector 101 is connected in the electrical circuit that drives a motor (not shown) so that the current flow to a connecting terminal 110 is from fixed contact 108 through bimetallic disk 104, fixed contact 107 and heater 109.
In a case where the rotor of a motor is locked or the motor is under excessive load, the ambient temperature rises and an electrical current larger than ordinary flows through bimetallic 104, with a result that, as shown in FIG. 6, the bimetallic disk reaches its actuation or snap temperature and snaps over center thereby moving contacts 105 and 106 out of contact with fixed contacts 107 and 108. Accordingly, the supply of electrical current to the motor is cut off and the motor is thus protected. Such protectors have been used widely, but it is always desirable to have an improved device. This fact is especially true for the protection of motors of compressors used in air conditioners, or the like, to better protect in the instances of leakage of cooling gas, or in the case of "end of life" failure of the device with contact welding between the movable and stationary contacts.